panic: Incrementing non-positive ref count

goroutine 1225904 [running]:
gvisor.googlesource.com/gvisor/pkg/refs.(*AtomicRefCount).IncRef(0xc4a8abf200)
	pkg/refs/refcounter.go:215 +0x79
gvisor.googlesource.com/gvisor/pkg/sentry/mm.(*MemoryManager).Fork(0xc4a8528000, 0x10cb800, 0xc423c97200, 0x0, 0x0, 0x0)
	pkg/sentry/mm/lifecycle.go:90 +0x892
gvisor.googlesource.com/gvisor/pkg/sentry/kernel.(*TaskContext).Fork(0xc423c97930, 0x10cb800, 0xc423c97200, 0x0, 0x3, 0x14566, 0x3)
	pkg/sentry/kernel/task_context.go:91 +0x2e4
gvisor.googlesource.com/gvisor/pkg/sentry/kernel.(*Task).Clone(0xc423c97200, 0xc4af92f8f8, 0x0, 0x0, 0x0, 0x0)
	pkg/sentry/kernel/task_clone.go:203 +0x2c3
gvisor.googlesource.com/gvisor/pkg/sentry/syscalls/linux.clone(0xc423c97200, 0x100000, 0x20003500, 0x200035c0, 0x20003600, 0x20003640, 0x42f108, 0xc420034000, 0x46154c, 0x852a58)
	pkg/sentry/syscalls/linux/sys_thread.go:157 +0x22f
gvisor.googlesource.com/gvisor/pkg/sentry/syscalls/linux.Clone(0xc423c97200, 0x100000, 0x20003500, 0x200035c0, 0x20003600, 0x20003640, 0x0, 0x47c9be, 0xc4af92fa88, 0x42f404, ...)
	pkg/sentry/syscalls/linux/sys_thread.go:171 +0x81
gvisor.googlesource.com/gvisor/pkg/sentry/kernel.(*Task).executeSyscall(0xc423c97200, 0x38, 0x100000, 0x20003500, 0x200035c0, 0x20003600, 0x20003640, 0x0, 0x0, 0x0, ...)
	pkg/sentry/kernel/task_syscall.go:162 +0x14f
gvisor.googlesource.com/gvisor/pkg/sentry/kernel.(*Task).doSyscallInvoke(0xc423c97200, 0x38, 0x100000, 0x20003500, 0x200035c0, 0x20003600, 0x20003640, 0x0, 0x100000, 0x46155c)
	pkg/sentry/kernel/task_syscall.go:280 +0x7e
gvisor.googlesource.com/gvisor/pkg/sentry/kernel.(*Task).doSyscallEnter(0xc423c97200, 0x38, 0x100000, 0x20003500, 0x200035c0, 0x20003600, 0x20003640, 0x0, 0xc42034ff60, 0xc4af92fc68)
	pkg/sentry/kernel/task_syscall.go:241 +0xc4
gvisor.googlesource.com/gvisor/pkg/sentry/kernel.(*Task).doSyscall(0xc423c97200, 0x2, 0xc420a1e900)
	pkg/sentry/kernel/task_syscall.go:216 +0x19f
gvisor.googlesource.com/gvisor/pkg/sentry/kernel.(*runApp).execute(0x0, 0xc423c97200, 0x10bc5a0, 0x0)
	pkg/sentry/kernel/task_run.go:219 +0x1502
gvisor.googlesource.com/gvisor/pkg/sentry/kernel.(*Task).run(0xc423c97200, 0x3f3a)
	pkg/sentry/kernel/task_run.go:95 +0x265
created by gvisor.googlesource.com/gvisor/pkg/sentry/kernel.(*Task).Start
	pkg/sentry/kernel/task_start.go:258 +0x194